The present invention relates to metals, in particular tantalum, and products made from tantalum as well as methods of making and processing the tantalum.
In industry, there has always been a desire to form higher purity metals for a variety of reasons. With respect to tantalum, higher purity metals are especially desirable due to tantalum""s use as a sputtering target and its use in electrical components such as capacitors. Thus, impurities in the metal can have an undesirable effect on the properties of the articles formed from the tantalum.
When tantalum is processed, the tantalum is obtained from ore and subsequently crushed and the tantalum separated from the crushed ore through the use of an acid solution and density separation of the acid solution containing the tantalum from the acid solution containing niobium and other impurities. The acid solution containing the tantalum is then crystallized into a salt and this tantalum containing salt is then reacted with pure sodium in a vessel having an agitator typically constructed of nickel alloy material, wherein tungsten or molybdenum is part of the nickel alloy. The vessel will typically be a double walled vessel with pure nickel in the interior surface. The salt is then dissolved in water to obtain tantalum powder. However, during such processing, the tantalum powder is contaminated by the various surfaces that it comes in contact with such as the tungsten and/or molybdenum containing surfaces. Many contaminants can be volatized during subsequent melting, except highly soluble refractory metals (e.g., Nb, Mo, and W). These impurities can be quite difficult or impossible to remove, thus preventing a very high purity tantalum product.
Accordingly, there is a desire to obtain higher purity tantalum products which substantially avoid the contaminations obtained during the processing discussed above. Also, there is a desire to have a tantalum product having higher purity, a fine grain size, and/or a uniform texture. Qualities such as fine grain size can be an important property for sputtering targets made from tantalum since fine grain size can lead to improved uniformity of thickness of the sputtered deposited film. Further, other products containing the tantalum having fine grain size can lead to improved homogeneity of deformation and enhancement of deep drawability and stretchability which are beneficial in making capacitors cans, laboratory crucibles, and increasing the lethality of explosively formed penetrators (EFP""s). Uniform texture in tantalum containing products can increase sputtering efficiency (e.g., greater sputter rate) and can increase normal anisotropy (e.g., increased deep drawability), in preform products.
A feature of the present invention is to provide a high purity tantalum product exhibiting a fine grain structure and/or uniform texture.
Another feature of the present invention is to provide articles, products, and/or components containing the high purity tantalum.
An additional feature of the present invention is to provide processes to make the high purity tantalum product as well as the articles, products, and/or components containing the high purity tantalum.
Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the description and appended claims.
To achieve these and other advantages, and in accordance with the purpose of the present invention, as embodied and broadly described herein, the present invention relates to tantalum metal having a purity of at least 99.995% and more preferably at least 99.999%. The tantalum metal preferably has a fine grain structure and/or uniform texture.
The present invention further relates to an alloy or mixture comprising tantalum, wherein the tantalum present in the alloy or mixture has a purity of at least 99.995% and more preferably at least 99.999%. The alloy or mixture (e.g., at least the tantalum present in the alloy or mixture) also preferably has a fine grain structure and/or uniform texture.
The present invention also relates to a high purity tantalum, e.g., suitable for use as a sputtering target, having a fully recrystallized grain size with an average grain size of about 150 xcexcm or less and/or having a primary (111)-type texture substantially throughout the thickness of the tantalum and preferably throughout the entire thickness of the tantalum metal and/or having an absence of strong (100) texture bands within the thickness of the tantalum.
The present invention further relates to manufacturing plate and sheet from the above-mentioned tantalum by flat-forging the tantalum, machining into rolling slabs, annealing rolling slabs, rolling into plate or sheet, then annealing the plate or sheet. Final products such as sputtering targets can be then machined from the annealed plate or sheet.
The present invention also relates to a sputtering target comprising the above-described tantalum and/or alloy. The sputtering target can also be formed by radial forging and subsequent round processing to produce billets or slugs, which are then forged and rolled to yield discs, which can then be machined and annealed.
The present invention further relates to resistive films and capacitors comprising the above-described tantalum and/or alloy.
The present invention also relates to articles, components, or products which comprise at least in part the above-described tantalum and/or alloy.
Also, the present invention relates to a process of making the above-described tantalum which involves reacting a salt-containing tantalum with pure sodium or other suitable salt in a reactive container or pot and an agitator which both are made from or have a liner comprising a metal or alloy thereof which has the same or higher vapor pressure as tantalum at the melting point of tantalum.
The present invention further relates to processing tantalum powder by melting the tantalum powder in a high vacuum of 10xe2x88x922 torr or more. The pressure above the melt is lower than the vapor pressures of the impurities existing in the tantalum. Preferably, the melting of the tantalum powder is accomplished by electron beam melting.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.